The present invention relates to environmental sealing of substrates in the electrical, electronics, telecommunications, power and related industries, particularly to sealing of electrical terminals or other contacts and wire splices.
An environmental seal may be provided in many ways. For example, the substrate to be sealed may be sealed by surrounding it with some sealed box or other enclosure, it may be tape wrapped, it may be painted or it may be coated or surrounded with bulk sealing composition. The present invention is preferably concerned with this last category. Such sealing may be provided to protect the substrate from various contaminants, and in the case of electrical contacts particularly from water.
A problem arises in providing environmental protection due to an inherent conflict between the desire for ease of installation of the sealing means, and tightness of the final seal. This problem is often overcome by having the sealing means undergo some change in physical condition, for example a paint may be applied as a liquid that subsequently solidifies. An alternative is the provision of a thermoplastic material, such as a hot-melt adhesive, that may be softened or melted and then applied to the substrate and allowed to solidify. Another example is a curable composition that in its pre-cured state has a low viscosity allowing it to be poured in place around the substrate, after which it is caused to cure.
For many applications, dimensionally heat-recoverable articles are used to provide rugged, long-lasting environmental seals. Such an article may be supplied in an expanded, enlarged, form in which it is positioned loosely around the substrate and then heated to cause it to shrink into tight engagement with the substrate.
Recently it has been proposed to provide an environmental seal by means of a sealing material that is supplied pre-cured in some form of container which is then fixed relative to the substrate so that the sealing material is held under pressure against a surface of the substrate to be sealed. This technique may be contrasted with one where a sealing material in an uncured form is poured into a container to surround the substrate and is then cured in situ. Pre-curing has many advantages, particularly ease and speed of installation in the field.
An apparatus for providing environmental sealing in this way is disclosed and claimed in U.S. Pat. No. 4,600,261 (Debbaut), the disclosure of which is incorporated herein by reference. That patent discloses a protection apparatus comprising:
(a) an insulating gel characterized by PA1 (b) first means to contain said gel; PA1 (c) second means to retain said gel within said first means; and PA1 (d) force means which acts on said first means so that said gel is maintained in compressive contact with said electrical contact and substantially encapsulates a conductive portion of said electrical contact, whereby upon release of said force means and a disengagement of said first means from said electrical contact, said gel remains substantially within said first means. PA1 (a) a gel, the gel being cured prior to coming into contact with any part of the substrate to be protected, the gel having a cone penetration value of 100-350 (10.sup.-1 mm) and an ultimate elongation of at least 200%; and PA1 (b) means for deforming the gel into close and conforming contact with the substrate. PA1 pressing together a substrate to be protected and an apparatus comprising a support member, a gel located on the support member, the gel being cured prior to coming into contact with any part of the substrate, the gel having a cone penetration value of 100 to 350 (10.sup.-1 mm) and an ultimate elongation of at least 200%, and means for deforming the gel into close and conforming contact with the substrate, the apparatus and the substrate being pressed together so that the gel contacts the substrate and is deformed into close and conforming contact therewith. PA1 (a) providing (preferably at ambient temperature) a sealing material having an ultimate elongation according to ASTMD 638-80 of at least 100%, preferably 200% to 300%, and a cone penetration according to ASTM D217-68 at 21.degree. C. of greater than 100 (10.sup.-1 mm); PA1 (b) subjecting the material to mechanical deformation in the presence of a solvent or suspending medium; and PA1 (c) then causing (preferably at ambient temperature) the material to flow over the surface of the substrate. PA1 (a) providing a material having an ultimate elongation according to ASTM D638-80 of at least 100%; and PA1 (b) fragmenting the material in the presence of a solvent or suspending agent.
(1) a cone penetration value from approximately 150-350 (10.sup.-1 mm); PA2 (2) an ultimate elongation of at least approximately 200%; PA2 (3) a maximum tensile strength of approximately 20 psi; PA2 (4) a cohesive strength greater than its adhesive strength;
U.S. Pat. No. 4,634,207, the disclosure of which is incorporated herein by reference, discloses an apparatus for protecting a substrate, comprising
Also disclosed is a process for protecting a substrate, comprising the steps of:
The use of sealing materials for environmental protection is also disclosed in the following patents, the disclosures of each of which are incorporated herein by reference: U.S. Pat. Nos. 4,643,924 (Uken et al.), 4,690,831 (Uken et al.), 4,581,265 (Follette), 4,610,910 (Follette), 4,610,738 (Jervis), 4,600,804 (Howard), 4,701,574 (Shimirak), U.S. Ser. No. 901,971 filed 29 Aug. 1986 (Dubrow) equivalent to EP-A-0194872, U.S. Ser. No. 859,171 filed 29 May 1986 (Kayset) equivalent to EP-A-0225370, U.S. Pat. Nos. 4,662,692 (Uken et al.), 4,647,717 (Uken), U.S. Ser. No. 767,555 (Story) filed 20 Aug. 1985 equivalent to EP-A-0213874, U.S. Ser. No. 801,018 (Gamarra) filed 22 Nov. 1985 equivalent to EP-A-0224389, and U.S. Ser. No. 945,219 (Chang) filed 22 Dec. 1986 equivalent to EP-A-0174165.
Cone penetration values in the above-mentioned specifications are unless the context otherwise requires or states, and are in this specification, expressed in units of 10.sup.-1 mm and are measured by ASTM D217-68 at 70.degree. F. (21.degree. C.) on an undisturbed sample using a standard 1:1 scale cone (cone weight 102.5 g, shaft weight 47.5 g), the penetration being measured after 5 seconds.
Ultimate elongation values in the above-mentioned specifications are unless the context otherwise requires or states, and are in this specification, as measured according to the technique of ASTMD 638-80 at 70.degree. F. (21.degree. C.) using a type 4 die to cut the sample and at a speed of 50 cm/minute.
A problem can arise in difficult circumstances with the above prior art sealing material (referred to in general terms herein as a "gel") and/or above prior art methods. That problem may arise where the substrate is of a complex shape since it may then be difficult to cause the gel fully to cover all surfaces of the substrate by forcing against the substrate a gel pre-cured or cast in a container. This is likely to be the case where the substrate is deep and must therefore penetrate a great distance into the gel, or where the substrate comprises many wires around which the gel must be caused to flow.
An alternative to pouring a liquid material around the substrate and then curing is likely to be unacceptable because it is impractical, time consuming and may result in the release of undesirable gasses during curing. The use of a hot-melt sealing material is frequently impractical due to the amount of heat required, and consequent possible damage to the substrate.
We have now found that this problem of installation of materials of the general type referred to as gels can be overcome by subjecting the material to mechanical deformation prior to use in the presence of a suitable solvent or extender or suspending medium. This then allows the material to be directed to the position where it is required, by for example extrusion through a nozzle. The step of extrusion itself may provide the desired mechanical deformation. We have found that the flow properties of the material may be suitably altered by this deformation, but that it may be able, where necessary, afterwards to cohere or to "knit" back together again, retaining a sufficient ultimate elongation or other property required during its service life.